Field of the Invention
The present disclosure relates to an image reading apparatus. More specifically, the present disclosure relates to an image reading apparatus capable of reading color images.
Description of the Related Art
Image reading systems for image reading apparatuses can be broadly classified into two systems: a charge coupled device (CCD), which is an optical reduction system, and a contact image sensor (CIS) system. Of the two systems, the CIS system can be further classified into two types. One type separates red, green, and blue light on a light projecting side and irradiates an object to be read such as a document with light. The other type separates light reflected from the object being read into red, green, and blue on a light receiving side.
The type that separates light into red, green, and blue on the light receiving side includes three reading sensors. The reading sensors include individual optical filters that separate the light into respective colors: red, green, and blue. In this way, an image separated from the object being read into each color, red, green, and blue, is obtained by the corresponding reading sensor.
By contrast, the type that separates red, green, and blue light on the light projecting side includes one reading sensor. By switching over red, green, and blue light sources consecutively, the corresponding light is emitted toward the object to be read. In this way, each time one of the light sources is illuminated, an image separated from the object being read into the corresponding color, red, green, or blue, is obtained by the reading sensor.
The type that separates red, green, and blue light on the light projecting side can serve to reduce manufacturing costs, since the number of reading sensors and optical filters used in this type is fewer than that in the type that separates light into red, green, and blue on the light receiving side.
The CIS system that separates red, green, and blue light on the light projecting side is disclosed in JP 07-250212 A (Patent Document 1). The configuration disclosed therein includes a white light source, a light shielding member, a cylindrical filter, and a drive section. The white light source illuminates a document. The light shielding member is disposed around the white light source and includes a slit at a position corresponding to the document. The cylindrical filter is arranged around the light shielding member and includes three primary colors of R, G, and B filters regularly and sequentially arranged therein in a circumferential direction. The drive section drives and controls the rotation of the filter so as to cause each of the R, G, and B filters to consecutively face the document surface in synchronization with the conveyance of the document.
However, the technique disclosed in JP 07-250212 A needs to include the cylindrical filter including R, G, and B optical filters around the white light source as well as the drive section that rotates the filter. Therefore, the technique may have an issue that not only does the size of an apparatus itself increase, but also manufacturing costs thereof increase.